Cemented carbide which contains tungsten carbide (WC) as a main component and added with carbide such as titanium (Ti) and tantalum (Ta) using cobalt (Co), nickel (Ni) and the like as bonding metal for the purpose of improving performance is excellent in hardness and abrasion resistance. Accordingly, such cemented carbide is suitably used for a cemented carbide tool for metal processing.
In this case, the cemented carbide tool which cannot be used any more due to chipping or abrasion and the chipped portion of the cemented carbide tool are to be discarded as hard scraps. Furthermore, part of cemented carbide powder produced in the process of manufacturing a cemented carbide tool and grinding dust and the like produced by the processing using the cemented carbide tool are to be discarded as soft scraps. These hard scraps and soft scraps contain a great amount of tungsten regarded as rare metal.
Thus, for example, a method for recycling a cemented carbide tool for recovering tungsten carbide from a used cemented carbide tool and the like is proposed in “Collection of Tungsten and the like from Waste Cemented Carbide Tool” (Metal Resources Report; Vol. 38, No. 4, pp. 407 to 413, November 2008) written by Yasuhiko Tenmaya issued by Rare Metal High Efficiency Collection System Development Project (Non-Patent Document 1). The method for recycling the cemented carbide tool disclosed in Non-Patent Document 1 is carried out as described below.
First, hard scraps and soft scraps of the cemented carbide tool are reacted with molten salt of sodium nitrate and then dissolved in water, to produce a sodium tungstate aqueous solution.
Then, an ion exchange method using ion-exchange resin is employed to produce an ammonium tungstate aqueous solution from the sodium tungstate aqueous solution. Then, ammonium paratungstate (APT) is crystallized out from the ammonium tungstate aqueous solution.
Then, the ammonium paratungstate crystallized out as described above is calcined, reduced and carbonized to thereby allow production of tungsten carbide.
Furthermore, for example, Japanese Patent National Publication No. 11-505801 (Patent Document 1) proposes to use molten salt containing 60 to 90 percent by mass of sodium hydroxide (NaOH) and 10 to 40 percent by mass of sodium sulfate (Na2SO4) for producing sodium tungstate by oxidizing the scraps of hard alloy and/or scraps of heavy metal in the molten salt. It also proposes that the reaction between the above-described scraps and molten salt occurs within a rotary kiln that is operated in a manner of batch processing and can be directly heated.